OTTAWA -- The federal Liberal government hasn't yet "landed" on its promised legislative option to push the Trans Mountain pipeline expansion forward, says Natural Resources Minister Jim Carr.

Justin Trudeau's government is "actively pursuing" legislation that will reassert Canada's constitutional authority to build and expand pipelines, the prime minister promised Sunday after an emergency meeting with the feuding premiers of B.C. and Alberta.

However, it hasn't yet figured out what it will look like.

"We're looking at legislative options," Carr said Wednesday on his way into the daily question period. "We haven't landed on one yet."

Government officials say it's not even yet clear which department will take the lead on the bill -- Natural Resources, Finance or Justice.

The plan, Carr said, is for legislation that would enhance the federal jurisdiction over pipelines -- something the government says is already crystal clear, which is why it has balked at the idea of launching a time-consuming reference to the Supreme Court of Canada.

Trudeau also dispatched Finance Minister Bill Morneau to strike a deal with pipeline builder Kinder Morgan to assuage investors now skittish about a project laden with possible court delays.

Kinder Morgan declared earlier this month it was halting all non-essential spending on the expansion, giving the government until the end of May to ensure the project would go ahead.

The expansion would build a second pipeline alongside an existing one, doubling its capacity to carry diluted bitumen from Alberta's oilsands to Kinder Morgan's Westridge Marine Terminal in Burnaby, B.C., where it would be loaded onto oil tankers for export.

The hope is most of it would be shipped to Asia, opening up new markets for Canada's oil beyond the United States, Canada's only real oil customer -- a situation Trudeau says forces Canada to take a big hit on the price it gets for the resource.

Fearing the many environmental unknowns that surround diluted bitumen, B.C. wants to restrict the pipe's capacity until more is understood about how the material might behave in a marine environment, how it can be cleaned up and how a major spill might impact ocean life.

B.C. Attorney General David Eby said his government will file a court reference by the end of April to determine if it can to stop the flow of dilbit, as diluted bitumen is known, on the grounds of its own jurisdiction over environmental concerns.

Not only does the oil itself pose a risk while in transit, environmental critics say, the expansion would increase oilsands development, exacerbating climate change. On Wednesday, Greenpeace activists welcomed Trudeau to London in a protest that featured a mock pipeline carrying "Crudeau oil."

Many environmental groups fear an increase in tanker traffic out of Burnaby along marine routes that are at times extremely narrow, worsening the risk of a major spill.

Carr played down that risk Wednesday, saying the expansion would only increase traffic by about one tanker a day, "surrounded by the most stringent marine policy in Canadian history."

Trudeau has said he only approved the pipeline in the context of balancing the need for environmental protections with the need for economic growth. The government's $1.5-billion Oceans Protection Plan is designed to account for such spills, he said, suggesting the government would make additional investments if need be.

Meanwhile, a new online survey by Angus Reid, conducted over the two days following Trudeau's Sunday meeting with the premiers, shows a modest increase in the number of respondents who support the pipeline, compared to a similar survey taken in February.

The polling industry's professional body, the Marketing Research and Intelligence Association, says online surveys cannot be assigned a margin of error as they are not random and therefore are not necessarily representative of the whole population.